Anamorphotic attachments for projection objectives are intended to provide a lens system ahead of a standard projection objective to apply an anamorphotic action to the projected beam.
For the most part such anamorphotic attachments for projection objectives have comprised four or more cylindrical lenses in two or more lens groups capable of generating a two-fold anamorphotic factor in the projection process over the projection from the basic objective alone.
For this purpose, the attachment is usually fixed on the front of the projection objective and has two relatively telescopingly movable parts, a movable one of which is axially shiftable relative to the other to provide the focusing action.
Hence one of the lens groups, usually the rear lens group, is fixed with respect to the projection objective while the other lens group, usually the front lens group, is axially movable. The lenses generally have smaller horizontal dimensions than vertical dimensions.
Anamorphotic attachments are used for the reproduction of anamorphotic films, for example, 35 mm--cinemascope films, and have been constructed at high cost heretofore with relatively large external dimensions. The outer diameter of the basic objective and the outer diameter of the anamorphotic attachment in the region of this connection to the objective are usually fixed dimensions or are predetermined. For motion picture projectors, these diameters are standardized.
Consequently it has been customary to provide anamorphotic attachments which widen from their attachment to the projection objective, i.e. from the rear end of the attachment, to the front side thereof. This has been found to complicate manipulation of the projection apparatus and the attachment. Since an anamorphotic attachment must be handled, smaller external dimensions are an advantage. In the past it has been found that complex adjustment mechanisms for the movable lens group have required large-size attachments which were expensive, difficult to manipulate and of complicated construction.
Indeed, with earlier constructions, it has not been possible to provide small dimensions of an anamorphotic attachment for a projection lens and still have available the space for the adjustment mechanisms which were necessary for it.